75 / 2024-04-10 15:38:46

Numerical Study on Decaying Arc Characteristics in CO2/C3H2F4 Gas Mixture with Different Gas Mixture Ratios

Gas circuit breaker,HFO-1234yf,CO2/C3H2F4 gas mixture,Free recovery condition,Gas flow rate

Currently, alternative SF₆ quenching gases has actively been researched to reduce the amount of SF₆ gas used in gas circuit breakers. A gas mixture of CO₂ with a small amount of C₄F₇N has been considered as one of the candidates in the world. However, one of the major suppliers of C₄F₇N has announced the discontinuation of production due to PFAS regulations. Therefore, it is necessary to further explore the possibility of different alternative arc quenching gases. As one candidate, HFO-1234yf (C₃H₂F₄) could be suitable for replacing SF₆ because of its boiling point of 243 K, a very low GWP of 4, and high dielectric strength. However, there is still a lack of relevant research data for arc extinguishing performance. It is thus necessary to study on understanding the properties of new different gases as well as arc-extinguishing properties. This study aims to understand the steady-state arc characteristics and transient arc characteristics in a CO₂/C₃H₂F₄ mixed gas flow.



In this report, numerical study was conducted to understand on arc behavior in CO₂/C₃H₂F₄ mixtures for various mixing ratios in steady state and free recovery conditions. First, particle composition of CO₂/C₃H₂F₄ mixture was calculated at different gas admixture ratio using molecular constants for C₃H₂F₄ and byproducts evaluated by quantum chemistry. Then, thermodynamic and transport properties of CO₂/C₃H₂F₄ gas mixture were also computed by Chapman-Enskog method. Using these data, numerical thermofluid simulations were conducted for decaying arc at different gas mixture ratios. This numerical thermofluid simulation calculates the two-dimensional distributions of gas flow and temperature in arc plasmas in CO₂/C₃H₂F₄ mixture flow in a steady state at arc current of DC 50 A. Then, using these steady-state thermofluid distributions as initial values, transient calculation was performed for decaying arcs in CO₂/C₃H₂F₄ mixture flow under free recovery condition. The gas mixture ratios were varied to 100%CO₂, 95%CO₂/5%C₃H₂F₄, 90%CO₂/10%C₃H₂F₄, 80%CO₂/20%C₃H₂F₄, and 100%C₃H₂F₄.



As a result, in the case of 100%C₃H₂F₄, the arc temperature decreased more rapidly than in 100%CO₂, increasing the arc resistance more rapidly than in 100%CO₂. This is due to the dissociation of high number density of C₃H₂F₄ in the low temperature region, resulting in a rapid temperature decrease due to the high peak of constant pressure specific heat at around 500 K. The significant increase in arc resistance is also attributed to the decrease in electron density due to the recombination reaction of CF⁺ and electron in temperature ranges from 7000 K to 3000 K. Even when up to 20%C₃H₂F₄ was mixed with CO₂, there was almost no difference in the arc temperature distribution and the time change in arc resistance, compared to the case with 100%CO₂. This is because, with a up to 20%C₃H₂F₄ mixture, the peak of constant pressure specific heat derived from the dissociation of CO₂ molecules in thermodynamic properties does not decrease. On the other hand, increasing mixing ratio of C₃H₂F₄ from 20% to more decreases the peak in specific heat derived from the dissociation of CO₂, resulting in faster arc decay.